Same word as virulency:

acerbity, acrimony, animosity, animus, annoyance, antagonism, bad feeling, bitterness, choler, cynicism, displeasure, dudgeon, embitterment, exacerbation, exasperation, fog, fury, gall, grudge, huff, hurt, ill feeling, ill will, indignation, ire, irritation, malice, malignity, miff, offense, outrage, passion, perturbation, pique, rage, rancor, rancorousness, resentfulness, rise, spite, umbrage, vehemence, vexation, virulence, wrath